The traditional Catholic understanding is that we are born with original sin and only baptism by a Catholic priest will save us from eternal hell fire, hence the practice of infant baptism.

From the Catholic Catechism-

The consequences of Adam's sin for humanity

402 All men are implicated in Adam's sin, as St. Paul affirms: "By one man's disobedience many (that is, all men) were made sinners": "sin came into the world through one man and death through sin, and so death spread to all men because all men sinned."[289] The Apostle contrasts the universality of sin and death with the universality of salvation in Christ. "Then as one man's trespass led to condemnation for all men, so one man's act of righteousness leads to acquittal and life for all men."[290]

403 Following St. Paul, the Church has always taught that the overwhelming misery which oppresses men and their inclination towards evil and death cannot be understood apart from their connection with Adam's sin and the fact that he has transmitted to us a sin with which we are all born afflicted, a sin which is the "death of the soul".[291] Because of this certainty of faith, the Church baptizes for the remission of sins even tiny infants who have not committed personal sin.[292]

404 How did the sin of Adam become the sin of all his descendants? The whole human race is in Adam "as one body of one man".[293] By this "unity of the human race" all men are implicated in Adam's sin, as all are implicated in Christ's justice. Still, the transmission of original sin is a mystery that we cannot fully understand. But we do know by Revelation that Adam had received original holiness and justice not for himself alone, but for all human nature. By yielding to the tempter, Adam and Eve committed a personal sin, but this sin affected the human nature that they would then transmit in a fallen state.[294] It is a sin which will be transmitted by propagation to all mankind, that is, by the transmission of a human nature deprived of original holiness and justice. And that is why original sin is called "sin" only in an analogical sense: it is a sin "contracted" and not "committed" - a state and not an act.

405 Although it is proper to each individual,[295] original sin does not have the character of a personal fault in any of Adam's descendants. It is a deprivation of original holiness and justice, but human nature has not been totally corrupted: it is wounded in the natural powers proper to it, subject to ignorance, suffering and the dominion of death, and inclined to sin - an inclination to evil that is called concupiscence". Baptism, by imparting the life of Christ's grace, erases original sin and turns a man back towards God, but the consequences for nature, weakened and inclined to evil, persist in man and summon him to spiritual battle.

406 The Church's teaching on the transmission of original sin was articulated more precisely in the fifth century, especially under the impulse of St. Augustine's reflections against Pelagianism, and in the sixteenth century, in opposition to the Protestant Reformation. Pelagius held that man could, by the natural power of free will and without the necessary help of God's grace, lead a morally good life; he thus reduced the influence of Adam's fault to bad example. The first Protestant reformers, on the contrary, taught that original sin has radically perverted man and destroyed his freedom; they identified the sin inherited by each man with the tendency to evil (concupiscentia), which would be insurmountable. The Church pronounced on the meaning of the data of Revelation on original sin especially at the second Council of Orange (529)[296] and at the Council of Trent (1546).[297]

http://www.scborromeo.org/ccc/p1s2c1p7.htm

Meanwhile, the original Reformers believed in Sola Scriptura AKA The Bible and the Bible Alone and tossed out Catholic traditions. They believed in the gift of grace from Jesus, and they believed you didn't need a priest to confess your sins, that you could have a personal relationship with the Savior of mankind.

Romans 5:12-21

12 Wherefore, as by one man sin entered into the world, and death by sin; and so death passed upon all men, for that all have sinned:

13 (For until the law sin was in the world: but sin is not imputed when there is no law.

14 Nevertheless death reigned from Adam to Moses, even over them that had not sinned after the similitude of Adam's transgression, who is the figure of him that was to come.

15 But not as the offence, so also is the free gift. For if through the offence of one many be dead, much more the grace of God, and the gift by grace, which is by one man, Jesus Christ, hath abounded unto many.

16 And not as it was by one that sinned, so is the gift: for the judgment was by one to condemnation, but the free gift is of many offences unto justification.

17 For if by one man's offence death reigned by one; much more they which receive abundance of grace and of the gift of righteousness shall reign in life by one, Jesus Christ.)

18 Therefore as by the offence of one judgment came upon all men to condemnation; even so by the righteousness of one the free gift came upon all men unto justification of life.

19 For as by one man's disobedience many were made sinners, so by the obedience of one shall many be made righteous.

20 Moreover the law entered, that the offence might abound. But where sin abounded, grace did much more abound:

21 That as sin hath reigned unto death, even so might grace reign through righteousness unto eternal life by Jesus Christ our Lord.

No need for a priest to confess our sins-

1 John 1:9

If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness.

The Reformers believed Christians are saved by faith in Jesus and not by works.

Ephesians 2:8-9

For by grace are ye saved through faith; and that not of yourselves: it is the gift of God: Not of works, lest any man should boast.

They believed works were important, not because they saved you, but because they were the fruit of the Spirit.

The traditional Catholic understanding is that we are born with original sin and only baptism by a Catholic priest will save us from eternal hell fire, hence the practice of infant baptism.

From the Catholic Catechism-

The consequences of Adam's sin for humanity

402 All men are implicated in Adam's sin, as St. Paul affirms: "By one man's disobedience many (that is, all men) were made sinners": "sin came into the world through one man and death through sin, and so death spread to all men because all men sinned."[289] The Apostle contrasts the universality of sin and death with the universality of salvation in Christ. "Then as one man's trespass led to condemnation for all men, so one man's act of righteousness leads to acquittal and life for all men."[290]

403 Following St. Paul, the Church has always taught that the overwhelming misery which oppresses men and their inclination towards evil and death cannot be understood apart from their connection with Adam's sin and the fact that he has transmitted to us a sin with which we are all born afflicted, a sin which is the "death of the soul".[291] Because of this certainty of faith, the Church baptizes for the remission of sins even tiny infants who have not committed personal sin.[292]

404 How did the sin of Adam become the sin of all his descendants? The whole human race is in Adam "as one body of one man".[293] By this "unity of the human race" all men are implicated in Adam's sin, as all are implicated in Christ's justice. Still, the transmission of original sin is a mystery that we cannot fully understand. But we do know by Revelation that Adam had received original holiness and justice not for himself alone, but for all human nature. By yielding to the tempter, Adam and Eve committed a personal sin, but this sin affected the human nature that they would then transmit in a fallen state.[294] It is a sin which will be transmitted by propagation to all mankind, that is, by the transmission of a human nature deprived of original holiness and justice. And that is why original sin is called "sin" only in an analogical sense: it is a sin "contracted" and not "committed" - a state and not an act.

405 Although it is proper to each individual,[295] original sin does not have the character of a personal fault in any of Adam's descendants. It is a deprivation of original holiness and justice, but human nature has not been totally corrupted: it is wounded in the natural powers proper to it, subject to ignorance, suffering and the dominion of death, and inclined to sin - an inclination to evil that is called concupiscence". Baptism, by imparting the life of Christ's grace, erases original sin and turns a man back towards God, but the consequences for nature, weakened and inclined to evil, persist in man and summon him to spiritual battle.

406 The Church's teaching on the transmission of original sin was articulated more precisely in the fifth century, especially under the impulse of St. Augustine's reflections against Pelagianism, and in the sixteenth century, in opposition to the Protestant Reformation. Pelagius held that man could, by the natural power of free will and without the necessary help of God's grace, lead a morally good life; he thus reduced the influence of Adam's fault to bad example. The first Protestant reformers, on the contrary, taught that original sin has radically perverted man and destroyed his freedom; they identified the sin inherited by each man with the tendency to evil (concupiscentia), which would be insurmountable. The Church pronounced on the meaning of the data of Revelation on original sin especially at the second Council of Orange (529)[296] and at the Council of Trent (1546).[297]

http://www.scborromeo.org/ccc/p1s2c1p7.htm

Meanwhile, the original Reformers believed in Sola Scriptura AKA The Bible and the Bible Alone and tossed out Catholic traditions. They believed in grace

Romans 5:12-21

12 Wherefore, as by one man sin entered into the world, and death by sin; and so death passed upon all men, for that all have sinned:

13 (For until the law sin was in the world: but sin is not imputed when there is no law.

14 Nevertheless death reigned from Adam to Moses, even over them that had not sinned after the similitude of Adam's transgression, who is the figure of him that was to come.

15 But not as the offence, so also is the free gift. For if through the offence of one many be dead, much more the grace of God, and the gift by grace, which is by one man, Jesus Christ, hath abounded unto many.

16 And not as it was by one that sinned, so is the gift: for the judgment was by one to condemnation, but the free gift is of many offences unto justification.

17 For if by one man's offence death reigned by one; much more they which receive abundance of grace and of the gift of righteousness shall reign in life by one, Jesus Christ.)

18 Therefore as by the offence of one judgment came upon all men to condemnation; even so by the righteousness of one the free gift came upon all men unto justification of life.

19 For as by one man's disobedience many were made sinners, so by the obedience of one shall many be made righteous.

20 Moreover the law entered, that the offence might abound. But where sin abounded, grace did much more abound:

21 That as sin hath reigned unto death, even so might grace reign through righteousness unto eternal life by Jesus Christ our Lord.

The Reformers believed Christians are saved by faith in Jesus and not by works.

Ephesians 2:8-9

For by grace are ye saved through faith; and that not of yourselves: it is the gift of God: Not of works, lest any man should boast.

They believed works were important, not because they saved you, but because they were the fruit of the Spirit.